1. Field of Invention
This invention relates generally to fuel injection systems, and more particularly to electronically controlled, solenoid operated fuel injection systems adapted for use with Diesel engines.
2. Prior Art
Diverse types of fuel injection systems have been utilized to deliver the precise amounts of fuel under high pressure necessity for optimum performance of Diesel engines. The systems shown in U.S. Pat. Nos. 3,908,621, granted Sept. 30, 1975, to Russell B. Hussey, and 3,952,711, granted Apr. 27, 1976 to John A. Kimberley et al, rely upon an engine generated variable "common rail," high pressure fluid to drive the fuel injectors in timed sequence. A central fuel metering and distributing apparatus delivers metered quantities of fuel to the injectors, which are actuated by an electric signal from a timing signal generator.
Another fuel injection system is shown in U.S. Pat. No. 3,835,829, granted Sept. 17, 1974, to Heinz Links. This system includes a reciprocating pump piston 19 performing its injection strokes by virtue of hydraulic pressure intermittently applied thereto in a controlled manner. Between injection strokes, the pump work chamber 43 is charged with pressurized fuel through a supply valve 21 and a throttle 22, which causes the charging period to be significantly longer than the injection period.
Another pertinent prior art fuel injection system is shown in U.S. Pat. No. 3,516,395 granted June 23, 1970 to Jacques Bassot et al. The fuel injection system in Bassot et al includes a fuel injection unit including a cylinder 8 and piston 7 of relatively large diameter dispose coaxially with, and above, a cylinder 6 and piston 5 of relatively small diameter. A pump 2 and an electronically controlled valve 3 supply a precisely measured charge of fuel to the small cylinder. Subsequently, in response to a signal from an electronic controller 12, fuel at supply pressure is admitted to the chamber above piston 7 to drive the piston 5 downwardly; such downward movement materially raises or amplifies the pressure level in the fuel in cylinder 6 and forces same to overcome the closing pressure in nozzle 14. The metered quantity of fuel is then discharged into the combustion chamber of an internal combustion engine.
A more compact electronically controlled, solenoid operated fuel injection system, in which several of the components including the solenoid, an intensifier piston, and the discharge nozzle are all encased in a common housing is shown in U.S. Pat. No. 3,921,604, granted Nov. 25, 1975 to Heinz Links. The Links '604 patent discloses a reciprocating pump piston 25 driven by a servo piston 24 which is intermittently exposed to fuel pressure to cause the pump piston to execute its delivery (injection) strokes. Between two delivery strokes, the pump work chamber 52 is charged with pressurized fuel through a throttle 26 while the pump piston executes its return stroke. The throttle 26 defines a permanently set flow passage so dimensioned as to substantially lengthen the charging period, with respect to the injection period, for the cycle of operation. The admission of fuel to the servo-piston is controlled by the switching positions of valve plunger 18, which, in turn is exposed to pressurized fuel for periods controlled by solenoid valve 17. The charging periods take place during the variable, de-energized periods of the solenoid valve.
Although the Links '604 represents a fuel injection system that is far superior to known hydraulically operated systems, as well as to other known electronically controlled systems, certain shortcomings are discernible. For example, the solenoid for each fuel injector in the Links '604 system is energized during most of the cycle of operation and this may lead to solenoid overheating, particularly at low engine speeds. Also, the valve plunger 18 in Links '604 is biased by a spring 19 against the force of supply pressure; if the spring breaks, or exhibits fatigue, during continued usage it will adversely influence the response of the valve plunger to the supply pressure. Perhaps, even more significantly, the fixed orifice 26 in the charging bore 48 affects the speed of the fuel supply into pump work chamber 52; the fixed orifice can not be adjusted to account for manufacturing tolerances and other differences among the individual injectors in the set of injectors utilized in a fuel injection system.
Another electronically controlled, solenoid operated fuel injection system is disclosed in U.S. Pat. No. 4,069,800, granted Jan. 24, 1978 to Fumio Kanada et al. This system suffers from operational deficiencies such as those encountered with the system shown in Links '604, e.g. the utilization of a spring 64 to bias the spool valve 62 to one end of a spool valve chamber. The bias of the spring reduces the sensitivity of the spool valve 62 to variations in the supply pressure, and augments the inertial effects acting upon the spool valve. This increases the response time necessary for the spool valve to be shifted to allow communication between the inlet port and the servo-chamber 54.